15,124 research outputs found
Control of a Circular Jet
The present study report direct numerical simulation (DNS) of a circular jet
and the effect of a large scale perturbation at the jet inlet. The perturbation
is used to control the jet for increased spreading. Dual-mode perturbation is
obtained by combining an axisymmetric excitation with the helical. In the fluid
dynamics videos, an active control of the circular jet at a Reynolds number of
2000 for various frequency ratios (both integer and non-integer) has been
demonstrated. When the frequency ratio is fixed to 2, bifurcation of the jet on
a plane is evident. However, for a non-integer frequency ratio, the
axisymmetric jet is seen to bloom in all directions.Comment: 2 page
Ultracold bosons in a synthetic periodic magnetic field: Mott phases and re-entrant superfluid-insulator transitions
We study Mott phases and superfluid-insulator (SI) transitions of ultracold
bosonic atoms in a two-dimensional square optical lattice at commensurate
filling and in the presence of a synthetic periodic vector potential
characterized by a strength and a period , where is an integer
and is the lattice spacing. We show that the Schr\"odinger equation for the
non-interacting bosons in the presence of such a periodic vector potential can
be reduced to an one-dimensional Harper-like equation which yields energy
bands. The lowest of these bands have either single or double minima whose
position within the magnetic Brillouin zone can be tuned by varying for a
given . Using these energies and a strong-coupling expansion technique, we
compute the phase diagram of these bosons in the presence of a deep optical
lattice. We chart out the and dependence of the momentum distribution
of the bosons in the Mott phases near the SI transitions and demonstrate that
the bosons exhibit several re-entrant field-induced SI transitions for any
fixed period . We also predict that the superfluid density of the resultant
superfluid state near such a SI transition has a periodicity () in
real space for odd (even) and suggest experiments to test our theory.Comment: 8 pages, 11 figures, v
Greener and sustainable method for alkene epoxidations by polymer-supported Mo(VI) catalysts
A polybenzimidazole supported Mo(VI) (PBI.Mo) catalyst has been prepared and characterised. The catalytic activities of the PBI.Mo catalyst in epoxidation of alkenes with tert-butyl hydroperoxide (TBHP) as an oxidant have been studied under different reaction conditions in a batch reactor. As alkene representatives we have chosen cyclohexene, limonene, α-pinene and 1-octene (a less reactive terminal alkene). The order of reactivity of the alkenes was found to be: cyclohexene>limonene>α-pinene>1-octene. The stability of each polymer catalyst was assessed by recycling a sample in batch reaction using conditions that will form the basis of the continuous process. The loss of Mo from each support has been investigated by isolating any residue from the reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions
Interacting spinor and scalar fields in Bianchi type-I Universe filled with viscous fluid: exact and numerical solutions
We consider a self-consistent system of spinor and scalar fields within the
framework of a Bianchi type I gravitational field filled with viscous fluid in
presence of a term. Exact self-consistent solutions to the
corresponding spinor, scalar and BI gravitational field equations are obtained
in terms of , where is the volume scale of BI universe. System of
equations for and \ve, where \ve is the energy of the viscous fluid,
is deduced. Some special cases allowing exact solutions are thoroughly studied.Comment: 18 pages, 6 figure
Nonlinear spinor field in Bianchi type-I Universe filled with viscous fluid: numerical solutions
We consider a system of nonlinear spinor and a Bianchi type I gravitational
fields in presence of viscous fluid. The nonlinear term in the spinor field
Lagrangian is chosen to be , with being a self-coupling
constant and being a function of the invariants an constructed from
bilinear spinor forms and . Self-consistent solutions to the spinor and
BI gravitational field equations are obtained in terms of , where
is the volume scale of BI universe. System of equations for and \ve,
where \ve is the energy of the viscous fluid, is deduced. This system is
solved numerically for some special cases.Comment: 15 pages, 4 figure
Design and evaluation of floating microspheres of amoxicillin trihydrate by ionotropic gelation method
The purpose of this investigation was to design and develop floating microspheres of Amoxicillin Trihydrate by ionotropic gelation method with combination of two polymers and to get the best possible formulation out of that with the various aspects. Floating drug delivery system have a bulk density less than gastric fluids and so remains buoyant in the stomach without affecting gastric emptying rate for a prolonged period of time. The floating microspheres were prepared using Ethyl cellulose and Hydroxy propylmethyl cellulose K4M as polymer to achieve an extended retention in upper GIT and there by improved bioavailability. The microspheres were evaluated for particle size analysis, Drug Entrapment Efficiency, Drug Loading Capacity, Floating efficiency, Swelling Study, Loose Surface Crystal Study , drug entrapment efficiency, drug- polymer compatibility study, Micromeritic properties like Bulk Density, Tapped Density, Carr’s Index, and Hausner’s Ratio, In-vitro release studies and surface morphology characterized by Scanning electron microscopy (SEM). The Microspheres have an average size range of 743.00±7.000 to 837.00±8.544μm. The entrapment efficiency was found to be in the range of 66.96±1.944 to 82.03±0.657 %. The In-vitro release studies of the drug from the best formulation F6 exhibited a sustained release of 93.46±0.684 % as studied over 10hrs. Release was best explained by zero-order kinetics model and it shows that the drug release follows diffusion mechanism. FT-IR data revealed that, compatible and there was no interaction between the drug and excipients added in the formulation. The data obtained in this study thus suggest that a floating microspheres of Amoxicillin Trihydrate are promising for sustained drug delivery which can reduce dosing frequency
Magnetic properties of PdAs2O6: a dilute spin system with an unusually high N\'eel temperature
The crystal structure and magnetic ordering pattern of PdAs2O6 were
investigated by neutron powder diffraction. While the magnetic structure of
PdAs2O6 is identical to the one of its isostructural 3d-homologue NiAs2O6, its
N\'{e}el temperature (140 K) is much higher than the one of NiAs2O6 (30 K).
This is surprising in view of the long distance and indirect exchange path
between the magnetic Pd ions. Density functional calculations yield
insight into the electronic structure and the geometry of the exchange-bond
network of both PdAs2O6 and NiAs2O6, and provide a semi-quantitative
explanation of the large amplitude difference between their primary exchange
interaction parameters
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